It has long been known within the packaging industry to employ packaging materials including outer layers of thermoplastic, which outer layers may be sealed to one another by fusion after heating and compression, for obtaining tight and durable sealing joints. The packaging material may thus, after forming, e.g. by folding or other means, be caused to retain its given configuration in that the outer layers of the packaging material are brought into abutment against one another and sealed to one another. One form of package production which has come into considerable use resides in the concept that a web of a packaging material (packaging laminate), comprising a core layer of paper or paperboard, a metal layer (normally aluminium) and layers of thermoplastic disposed outermost, is formed into a tube by the longitudinal edges of the web being brought together to one another in an overlap joint, whereafter the web edges are sealed to one another. The thus formed tube may then be filled with the contemplated contents, e.g. a liquid, whereafter the tube filled with liquid may be divided into individual containers by transverse sealing of the tube along narrow zones which are applied at uniform spacing from each other. The sealed tube sections can, prior to or in connection with the transverse sealing, be given a permanent configuration, e.g. a parallelepipedic configuration, by folding of the material, whereafter the closed tube sections can be separated from the remainder of the tube and form an individual, finished consumer package.
It is known to facilitate the sealing of the packaging material by utilising an inductor which consists of an electric conductor to which the desired form has been imparted and which forms one or more coil turns and which is connected to a current source which supplies the coil with high frequency alternating current. When this high frequency alternating current is led through the coil or inductor, a high frequency magnetic field occurs around it, and when the coil is placed adjacent a material containing a metal layer, induction currents are induced in this metal layer, which give rise to thermal energy in those parts of the metal layer which lie proximal the coil. By the generated heat, a layer of thermoplastic material, e.g. polyethylene, lying adjacent the metal layer will soften or melt. When two such layers of thermoplastic material are compressed against each other, the thermoplastic layers, in the region of the heating, will fuse together for the formation of a tight and durable joint. The width of the joint will, in this instance, be as wide as the coil wire/inductor conductor which abuts against the packaging material.
Prior art apparatuses for induction sealing of strips and longitudinal joints certainly function well, but in, for example, the development of high speed output machines, there is room for improvement in particular because of problems relating to the compression and the time which is required for the sealing operation. There is also a need in the art for a sealing apparatus which may be utilised for the spot heating of a clearly defined area, preferably on a moving material web. Also in connection with the development of opening arrangements for packages, there is a need for a sealing apparatus which may be utilised for spot heating.
Another problem in connection with the production of packages or packaging laminates is to be able to remove loose material, so called confetti, when an emptying hole is prefabricated through which the package is intended to be emptied of its contents. In such instance, a prefabricated emptying hole is made only partly, by means of incision lines through the packaging laminate, from the one side of the laminate, i.e. through a paper or paperboard web coated with a liquid-tight coating, but not through a subjacent metal foil. The problem in such instance is to be able, in a thoroughly controlled manner, to remove the formed parts of the coated paper or paperboard, i.e. the confetti, located inside the incision lines and which are still laminated to the metal foil. The technique for making prefabricated emptying holes is described in the applicant's copending patent application SE-AO-9903315, whose contents are hereby incorporated by reference.